// 一个数组已知元素的个数以及每个元素的数据类型
let x: [number, string] = [1, 'a']
// let y: [number, string] = ['1', 100]
interface IUser {
  username: string
}

let y: [number, IUser] = [ 1, { username: '吴大勋'}]

let z: [number, number[]] = [ 1, [ 2, 3, 4]]
let a: [number, Array<number>] = [ 1, [ 2, 3, 4]]